The corneal vertices of a subject are important points when determining centration parameters for fitting spectacles. Centration parameters are used to correctly arrange or center spectacle lenses in a spectacle frame such that the spectacle lenses are arranged at the correct position relative to the eyes of the spectacles-wearing person. Here, these are in part anatomical parameters of the relevant person, such as, the interpupillary distance, in part purely frame-specific parameters, such as, the frame disk width or the frame disc height, and in part combinations of anatomical and frame-specific parameters, such as, the vertex distance and the fitting point height. An overview of conventional centration parameters is provided by DIN EN ISO 13666, dated October 2013.
An at least approximate determination of the position of the corneal vertex in space and, typically, of the position of both corneal vertices in space, may be used advantageously in a further evaluation for determining centration parameters, in particular, for determining the vertex distance. Previously, the corneal vertex positions were manually annotated in the frontal and lateral images. Here, a reflection-based or pupil-based annotation was favored, depending on the preference of the optician. In the case of the reflection-based annotation, a light reflection is produced on the pupil with the aid of an LED, the light reflection being easier to detect than the pupil center. However, many opticians continue to prefer the pupil-based annotation.
A method of the type set forth at the outset is known from US 2011/0007269 A1. In this method, just like in the methods known from US 2003/0123026 A1, JP 2007/206211 A and US 2007/195266 A1, use is made of stereo algorithms, which are based on finding correspondences in images. A precondition in each case is a large overlap of the images, and so the selection of camera arrangements is greatly restricted. Here, arranging the cameras with very different recording directions in space is not possible.